This invention relates to an electrical control device applicable for example in adjusting the volume and/or tuning of an amplifier or radio receiver or for controlling lighting or power circuits.
In the design of conventional electronic equipment considerable attention is normally given to the provision of controls which are aesthetically pleasing and easy to manipulate. Such controls often amount for a significant proportion of the cost of the equipment.
One known control system uses a linearly arranged potentiometer. The sliding contact of this is connected to a member which projects through a slot in the front panel of the apparatus and is manipulated by hand. A certain amount of effort is required in moving the contact to overcome the resistance required to hold it in the position to which it is set. Also the front panel can be quite complicated to manufacture, particularly if several potentiometer controls are to be mounted on it.
The primary object of the invention is to eliminate the necessity of making a positive effort in adjusting the controls: i.e. to make adjustment as simple as possible. Accordingly the invention provides electrical apparatus comprising a continuously variable control device which is adapted to be changed by the user from a normal condition to a chosen condition by applying his finger and which is adapted to revert to its normal condition on the removal of the finger, the said apparatus also including means to store information for electrical control purposes representing the position of the said finger in relation to the device prior to removal. Because there is no need for friction between a potentiometer contact and the potentiometer resistor in order to hold the contact in its set position, adjustment can be made much simpler.
In a preferred form of the invention the control device includes two members accessible from outside the device and arranged so that they can be bridged at different positions by the tip of one's finger, at least one of the members being a resistor member. It is convenient to make one of the two members in the form of a resistor and the other as a relatively non-resistive conductor. In this arrangement a source of potential is connected across the resistor member which is used as a potential divider, the finger acting as a bridge to tap the different potentials appearing along the resistor to the conductive member.
It is a relatively simple matter to arrange for a signal, given when the finger is removed, to be used to lock the information in the store.
Where the control device is formed by two members, one of which is a resistor, these members may be constituted by a layer of conductive ink applied to an insulating backing material e.g. by screen printing. When applied to such apparatus as a radio, amplifier, television ect. only one control device need be used for several functions e.g. volume, tuning and tone controls. Separate stores must however be provided and means for switching them in turn to the control device so that the content of each store can be separately adjusted.